Physicists create clouds of impenetrable gases that bounce off each other

Apr 13, 2011 by Anne Trafton

Two gas clouds (one red and one blue), each a million times thinner than air, are seen to completely repel each other under the influence of strong, quantum-mechanical interactions. Such gas clouds can model matter under extreme conditions, such as neutron stars or the quark-gluon plasma of the early universe. Image: Martin Zwierlein

(PhysOrg.com) -- When one cloud of gas meets another, they normally pass right through each other. But now, MIT physicists have created clouds of ultracold gases that bounce off each other like bowling balls, even though they are a million times thinner than air  the first time that such impenetrable gases have been observed.

While this experiment involved clouds of lithium atoms, cooled to near absolute zero, the findings could also help explain the behavior of similar systems such as neutron stars, high-temperature superconductors, and quark-gluon plasma, the hot soup of elementary particles that formed immediately after the Big Bang. A paper describing the work will appear in the April 14 issue of Nature.

The researchers, led by MIT assistant professor of physics Martin Zwierlein, carried out their experiment with an isotope of lithium that belongs to a class of particles called fermions. All building blocks of matter  electrons, protons, neutrons and quarks  are fermions.

Different states of fermionic matter are distinguished by their mobility. For example, electrons can be mobile, as in a metal; immobile, as in an insulator; or flow without resistance, as in a superconductor. However, for many types of material, including high-temperature superconductors, it is not known what circumstances induce fermions to form a given state of matter. This is especially true of materials with strongly interacting fermions, meaning they are more likely to collide with each other (also called scattering).

In this study, the researchers set out to model strongly interacting systems, using lithium gas atoms to stand in for electrons. By tuning the lithium atoms' energy states with a magnetic field, they made the atoms interact with each other as strongly as the laws of nature allow, meaning that they scatter every time they encounter another atom.

To eliminate any effects of heat energy, the researchers cooled the gas to about 50 billionths of one Kelvin, close to absolute zero (-273 degrees Celsius). They used magnetic forces to separate the gas into two clouds, labeled "spin up" and "spin down, then made the clouds collide in a trap formed by laser light. Instead of passing through each other, as gases would normally do, the clouds repelled in dramatic fashion.

"When we saw that these ultra dilute puffs of gas bounce off each other, we were completely amazed," says graduate student Ariel Sommer, lead author of the Nature paper.

The gas clouds did eventually diffuse into each other, but in several cases it took an entire second or more  an extremely long time for events occurring at microscopic scales.

The research, conducted at the MIT-Harvard Center for Ultracold Atoms, is part of a program aimed at using ultracold atoms as easily controllable model systems to study the properties of complex materials, such as high-temperature superconductors and novel magnetic materials that have applications in data storage and improving energy efficiency.

In future work, the researchers plan to confine the lithium gases to two-dimensions, which will allow them to simulate the two-dimensional state in which electrons exist in high-temperature superconductors.

Their work can also be used to model the behavior of other strongly interacting systems, such as high-density neutron stars, which are only a few tens of kilometers in diameter but more massive than our sun.

Another substance that interacts as strongly as the atoms in the ultracold lithium gas clouds created at MIT is quark-gluon plasma, which existed at the universe's formation and has been recreated in particle colliders by colliding atomic nuclei at energies corresponding to a trillion degrees.

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User comments : 6

ZephirAWT

I'm currently working on trying to build up a theory to try and unify physics (yeah pretty ambitious lol)... It's interesting to hear about these ground state effects, because it's the sort of thing my hypothesis produces at low excitation levels.

No, I won't be more specific. It's nowhere near a point where it can actually make mathematical predictions, and I don't want to embarrass myself.

EDIT: Meh, I may as well give a hint so as not to be an ass... My theory basically tries to plot particles within a phase space - basically it's a version of the Lagrangian where everything is quantized, including space and time.

We can see, how the condensates of bosons are colliding and bouncing like the fermions.

The article says:

The researchers, led by MIT assistant professor of physics Martin Zwierlein, carried out their experiment with an isotope of lithium that belongs to a class of particles called fermions

Thus, the gas clouds are not BECs.

Well, what did you expect? This is Zephir we're talking about. No other member exhibits such an ability to systematically misunderstand articles and posts. The article says lithium atoms in the very first sentence and he calls them bosons. The article is about thin ultra cold gases that manage to repel each other and he confuses this with BECs. Hey, Zeph, Bose was the guy's *name*. Here's an idea: how about we name the particles that permeate space in AWT bozos? That will provide us with an accurate picture of where Dense AWT stands as it will then be said to be populated by Dense Bozos who squark, squark, squark all day long.

ZephirAWT

BTW You may need to be so frustrated from aether theory - this theory is here for just you.

Oh stop! You're going to make me feel all warm and fuzzy inside. Frustrated? Please. Between you, the other cranks and the Creationist polluting this science site, I'll admit to being mildly exasperated. But I'm not American so I don't have to live with the full brunt of scientific idiocy being thrust into my face daily in the form of IDers, YECs, Cold Fusion Wankers (though they seem to have moved to Italy of late), and other cranks trying to seize control of the local school-boards, preaching Faith-based "science", acting like the scientific method is political pamphlet, and treating the Bible like it's a physics book. So no, it hasn't actually come to the level of general frustration yet. Just because it's not yet that personal. Still, exasperation can be sufficient motivation.

IMO the cold fusion of hydrogen and nickel can work at room temperature, because the repulsive Coulomb barrier is relevant for naked nickel nuclei only, i.e. these completely ionized one. The atom nuclei stripped of all electrons can be prepared easily at the case of lightweight atoms, like the hydrogen or hellium - but heavier atoms are surprisingly reluctant against the complete lost of their electrons. The energy (density) required for complete ionization of nickel nuclei is comparable to the energy density required for its fission - which basically means, the electrons at the bottom of nickel orbitals are forming the nearly homogeneous energetic continuum with the underlying atom nuclei. So, when the nickel atom is full of electrons, these electrons are balancing/shielding the repulsive forces of atom nuclei for tiny proton, which could literally "swim" through nickel orbitals into its core.